Alternate: Engineering Sustainability and Modernization Efforts into Wastewater Systems - The Case of the Great Hills Lift Station in Austin, Texas

The City of Austin's water and wastewater utility, Austin Water, operates 143 lift stations and manages a sprawling network of approximately 2,927 miles of wastewater pipelines. Among these is the Great Hills Lift Station, located at 9009 ½ Spicebush Drive, which has reached the end of its expected service life. This station, positioned within an environmentally sensitive area near the Bull Creek tributary, plays a critical role in wastewater management and supports the City's vision for sustainable infrastructure. Given its current state, the rehabilitation and replacement of this facility have been prioritized under Austin Water's efforts to ensure resilient wastewater services for the future. Lift stations like Great Hills are integral to Austin Water's system, serving to pump wastewater from low-lying areas to higher elevations where gravity can aid its movement. With over three decades of operation since its construction in 1985, the Great Hills Lift Station has become a focal point for infrastructure upgrades. Its modernization aligns with recommendations from the 2021 Winter Storm Uri After Action Report, underscoring the need for reliable facilities considering extreme weather events. Background and Location The Great Hills Lift Station occupies a wastewater easement at the end of a narrow, 300-foot driveway nestled between two residential properties. The site, approximately 15 feet north of the 100-year floodplain, is within Water Quality Transition Zone and adjacent to Bull Creek. Its location presents unique challenges for construction and maintenance due to steep access, environmental restrictions, and proximity to residential properties. These factors demand careful evaluation of design alternatives to minimize disruption while meeting operational and environmental standards. Existing Infrastructure The current facility includes two 10-foot diameter concrete wet wells, 220-square-foot dry pit reaching a depth of 31 feet, and two 150-horsepower pumps. Additionally, the station incorporates electrical equipment, instrumentation panels, and flowmeter vault located outside its fenced boundary. Wastewater flows into the lift station via three gravity mains and is pumped out through 16-inch ductile iron force main. However, the aging infrastructure and operational constraints necessitated a comprehensive upgrade to meet modern standards. Feasibility Study and Design Alternatives Austin Water engaged K Friese + Associates (KFA) to evaluate improvement options for the lift station. Four primary alternatives were explored: 1. Reusing the existing wet well & This would involve structural evaluations, cleaning, and modifications. However, the site's environmental and access limitations rendered this option impractical and cost-prohibitive. 2. Constructing a bypass tunnel & A 4,500-foot tunnel bypassing the lift station was considered but was dismissed due to high costs and anticipated construction challenges. 3. Building a new wet well east of the existing site & This option involves rehabilitating the northern wet well to collect inflows and constructing a new wet well within the current wastewater easement. 4. Building a new wet well west of the existing site & While feasible, this would require additional easement acquisition, adding complexity and cost. After evaluation and discussions with the City, the east site layout was selected as the most viable solution. This plan ensures minimal disruption to the surrounding area while addressing operational and environmental requirements. Proposed Project Features The new design includes the installation of a 12-foot diameter polymer concrete wet well, replacing the originally proposed 16-foot diameter wet well to accommodate site access constraints. Additional components include concrete valve vault with stainless steel access hatches, 10-foot jib crane, and modernized electrical panels. A 12-foot retaining wall will improve site accessibility and stabilize the area. The project also integrates odor control measures, force main upgrades, and a water quality pond to offset increased impervious cover. Pump Selection and Electrical Enhancements System curves were developed to select pumps capable of handling a flow rate of 2,000 gallons per minute (GPM), slightly exceeding the station's current capacity of 1,890 GPM. To comply with City of Austin and Texas Commission on Environmental Quality (TCEQ) standards, the design includes one operational pump and one backup pump for redundancy. Electrical improvements feature a natural gas generator, replacing the original diesel-powered unit, to align with sustainability goals. Coordination with Texas Gas was instrumental in ensuring the availability of natural gas for the generator. Environmental Considerations The project site's sensitive ecological setting necessitated thorough environmental assessments. Species such as the Golden-Cheeked Warbler, Jollyville Plateau Salamander, and endangered karst invertebrates were identified in the area. Consequently, construction timelines were extended from 18 to 30 months to accommodate nesting periods and implement stormwater controls to protect local wildlife. Tree mitigation measures, including the preservation of heritage trees and replanting native species, were also incorporated. Permitting and Community Involvement Obtaining the required permits was multifaceted process due to the site's location within Critical Water Quality Zone (CWQZ) of Bull Creek. Variances from the City of Austin's Land Development Code were necessary to proceed with the project. Additionally, extensive neighborhood outreach was conducted to address community concerns and maintain transparency throughout the pre-construction phase. Construction Progress and Challenges Construction began in November 2024, with completion anticipated by August 2026. Key milestones include the placement of the new wet well and the casting of the valve vault, while the existing lift station remains operational. However, the project has faced challenges, including: - Staffing continuity issues: Turnover among City personnel required the design team to prioritize knowledge retention by maintaining consistent leadership. - Restricted workspace: Limited easement boundaries and steep access necessitated innovative construction sequencing and real-time coordination with operators. - Supply chain disruptions: Delays in materials prompted the team to implement adaptive procurement strategies to stay on schedule. Lessons Learned and Broader Impact The Great Hills Lift Station project illustrates the complexities of modern wastewater infrastructure upgrades in environmentally sensitive areas. By balancing community needs, environmental stewardship, and engineering innovation, this project sets precedent for future improvements within the City of Austin's wastewater system. Adaptive design strategies, phased execution, and sustainability-focused solutions highlight the importance of strategic planning and collaboration in addressing urban infrastructure challenges.